The amphibious aircraft had been imported in kit form and assembled by the owner. Several uneventful flights had been conducted in the landplane configuration. The aircraft was then operated from a nearby river for water handling evaluation, and for the owner to obtain a floatplane endorsement. On the fourth takeoff, just before the aircraft was about to lift off the water, it rapidly nosed over and sank. The owner managed to escape from the aircraft immediately, but the training pilot was temporarily trapped and had to be cut from his seat belt. Neither of the occupants were injured in the accident. Inspection of the wreckage revealed that the forward section of the planing hull had failed. The failed section then acted as a water scoop, which resulted in the rapid nose over. A subsequent investigation of the wreckage by the manufacturer confirmed that the fibreglass reinforced plastic hull did not meet design specification. Two of the required three layers of woven glass cloth had been omitted from both sides of the foam core during the manufacture of the hull, greatly reducing its strength.